Spatial and Temporal Stress Variations before and after the 2008 Wenchuan M_(w)7.9 Earthquake and its Implications:A Study based on Borehole Stress Data  

作　　者：MENG Wen LIN Weiren CHEN Qunce LI Yonghua 

机构地区：[1]Institute of Geophysics,China Earthquake Administration,Beijing 100081,China [2]Key Laboratory of Earthquake Source Physics,China Earthquake Administration,Beijing 100081,China [3]Key Laboratory of Active Tectonics and Geological Safety,Ministry of Natural Resources,Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China [4]Graduate School of Engineering,Kyoto University,Kyoto,Japan

出　　处：《Acta Geologica Sinica(English Edition)》2023年第1期226-242,共17页地质学报（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant No.41702351);the China Geological Survey Project(Grant Nos.DD20211376,DD20221816)。

摘　　要：In situ stress measurement data was analyzed to estimate the temporal and spatial stress variations at shallow depths in the Longmenshan fault zone(LMSF),prior to and following the 2008 Wenchuan earthquake(WCEQ).Analysis of the stress field related to fault strength and behavior is useful for understanding geodynamic processes and conducting hazard assessments.The shallow stress changes after the WCEQ show clear along-strike variations.Degrees of stress orientation rotations have a negative correlation with the horizontal principal stress ratios and the WCEQ apparently reduced the magnitude difference between horizontal principal stresses.Taking stress magnitudes and orientation distribution relative to the fault strike into account,we propose an intermediate-strength of LMSF,with a friction coefficient generally constrained between 0.35 and 0.6.In addition,high-pressure fluids in the fault zone reduce the effective normal stress and to a certain degree weaken the fault strength.The accumulated stress over a certain period following release of the WCEQ indicates the start of another earthquake cycle.The changing crustal stress field makes the LMSF stable or slipping optimally during geodynamic processes.The segmentation feature of the shallow crustal stress field in the LMSF may imply a different tectonic loading and seismic release processes along the fault.The southwestern section to the epicenter of the WCEQ favors the occurrence of future earthquakes,as highμm in a state of critical failure was present in this area,which indicates that the Wenchuan and Lushan earthquakes did not release the accumulated stress to a sufficient extent there.

关 键 词：stress variation in situ stress measurement fault strength hazard assessment Longmenshan fault zone 

分 类 号：P315.7[天文地球—地震学]